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MANAGERS AND PROJECTIONISTS 1151
storage batteries with each equipment are used as filters to smooth out generator ripple. They are not used as a source of power.
AMPLIFIERS— TYPES "B" (SPU), "C" AND "D." — RCA Photophone manufactures three types of amplifiers which are operated from a regular 100-volt, alternating current lighting circuit. The smallest of these is known as Type "D." It is installed in houses with a seating capacity of 750 or less. With this type equipment two RCA Photophone projectors or two professional projectors with Photophone sound attachments are installed. The same applies to the Type "C" equipment which is used for houses seating up to 1,500, and the Type "B" (SPU) for houses larger than 1,500.
With each of these equipments an input control panel is located on the front wall of the projection room. This panel has meters and rheostats for controlling the current in the photo-cell exciter lamps ; a change-over potentiometer (Fader) for changing from one projector to the other; a volume control and a volume indicating meter. Unlike the two equipments previously described, these types have no high voltage lines entering from the outside, but are constructed with rectifying units for supplying plate voltage. The three types are essentially the same, the only difference being in the number of units installed.
The Type "D" equipment has one voltage amplifier unit and one power amplifier unit. It operates four 12-inch dynamic cone loud-speakers. The Type "C" equipment has two voltage amplifier units, one of which is not in use but is held as reserve equipment, and two power amplifier units, both of which are in use feeding